Function Key Resources
Function key resources (of the 'FKEY' resource type) are
Command-Shift-number key combinations that are captured and processed by
the WaitNextEvent function. The screen utility resource 'FKEY' 3 now produces a screen shot, contained in a 'PICT' file, when the user presses
Command-Shift-3. 'FKEY' resource IDs 0 through 4 are reserved for future
use by Apple.